netdev - Re: [PATCH net] cxgb4: fix throughput drop during Tx backpressure

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Message-Id: <20200319.212950.742799321773945249.davem@davemloft.net>
Date:   Thu, 19 Mar 2020 21:29:50 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     rahul.lakkireddy@...lsio.com
Cc:     netdev@...r.kernel.org, nirranjan@...lsio.com, vishal@...lsio.com,
        dt@...lsio.com
Subject: Re: [PATCH net] cxgb4: fix throughput drop during Tx backpressure

From: Rahul Lakkireddy <rahul.lakkireddy@...lsio.com>
Date: Thu, 19 Mar 2020 23:08:09 +0530

> commit 7c3bebc3d868 ("cxgb4: request the TX CIDX updates to status page")
> reverted back to getting Tx CIDX updates via DMA, instead of interrupts,
> introduced by commit d429005fdf2c ("cxgb4/cxgb4vf: Add support for SGE
> doorbell queue timer")
> 
> However, it missed reverting back several code changes where Tx CIDX
> updates are not explicitly requested during backpressure when using
> interrupt mode. These missed changes cause slow recovery during
> backpressure because the corresponding interrupt no longer comes and
> hence results in Tx throughput drop.
> 
> So, revert back these missed code changes, as well, which will allow
> explicitly requesting Tx CIDX updates when backpressure happens.
> This enables the corresponding interrupt with Tx CIDX update message
> to get generated and hence speed up recovery and restore back
> throughput.
> 
> Fixes: 7c3bebc3d868 ("cxgb4: request the TX CIDX updates to status page")
> Fixes: d429005fdf2c ("cxgb4/cxgb4vf: Add support for SGE doorbell queue timer")
> Signed-off-by: Rahul Lakkireddy <rahul.lakkireddy@...lsio.com>

Applied and queued up for -stable.